The invention relates generally to aviation gasoline (Avgas) compositions and methods of making and using such compositions. More particularly, the present invention concerns high octane Avgas compositions containing a non-leaded additive package and methods of making and using such compositions.
Conventional aviation gasoline (Avgas) generally contains an aviation alkylate basefuel and a lead-based additive package. The industry standard Avgas known as 100 Low Lead (100LL) contains the lead additive tetraethyllead (TEL) for boosting the anti-knock property of the Avgas over the inherent anti-knock property of its aviation alkylate basefuel. Knocking is a condition of piston-driven aviation engines due to autoignition, the spontaneous ignition of endgases (gases trapped between the cylinder wall and the approaching flame front) in an engine cylinder after the sparkplug fires. A standard test that has been applied to measure the anti-knock property of lead-based Avgas under various conditions is the motor octane number (MON) rating test (ASTM D2700). Another standard test applied to lead-based Avgas is the supercharge (performance number) rating test (ASTM D909).
Despite the ability of lead-based Avgas to provide good anti-knock property under the severe demands of piston-driven aviation engines, such lead-based compositions are meeting stricter regulations due to their lead and lead oxide emissions. Current U.S. regulations set a maximum amount of TEL for aviation fuels at 4.0 ml/gal and concerns for the negative environmental and health impact of lead and lead oxide emissions may effect further restrictions. Gaughan (PCT/US94/04985, U.S. Pat. No. 5,470,358) refers to a no-lead Avgas containing an aviation basefuel and an aromatic amine additive. The Avgas compositions exemplified in Gaughan reportedly contain an aviation basefuel (e.g., isopentane, alkylate and toluene) having a MON of 92.6 and an alkyl- or halogen-substituted phenylamine that boosts the MON to at least about 98. Gaughan also refers to other non-lead octane boosters such as benzene, toluene, xylene, methyl tertiary butyl ether, ethanol, ethyl tertiary butyl ether, methylcyclopentadienyl manganese tricarbonyl and iron pentacarbonyl, but discourages their use in combination with an aromatic amine because, according to Gaughan, such additives are not capable by themselves of boosting the MON to the 98 level. Gaughan concludes that there is little economic incentive to combine aromatic amines with such other additives because they would have only a very slight incremental effect at the 98 MON level.
It would be desirable to find alternative Avgas compositions that avoid the use of lead-based additives and have good performance in piston-driven aviation engines. It would also be desirable to find Avgas compositions that could use less expensive basefuels.